It's my understanding that the widths are the same until 1972, is that correct?
Bought '66 F-250 and it has the original 4.10 gears--screams too much for me. Its my understanding that starting in 1968 on the F-250, an optional 3.54 or 3.73 gears were available. I would prefer to leave the original drivetrain (352 & granny 4 speed) intact rather than going the AOD route. Thanks guys.

 

1957/65 F250 Dana 60: 4.10-1 - 4.56-1 - 4.88-1.

3.54-1 & 3.73-1 introduced in 1966 F250 Dana 60's. Other ratios still available.

None of these ratios were optional, all were RPO's (Regular Production Orders).

But most people back then didn't want 3.54-1, making it a difficult ratio to find today.

The scenario changed during the 1st Arab Oil Embargo of 1973/74. For the first time since during WWII, people were concerned about MPG

2nd Arab Oil Embargo occurred in 1979. Here in LA LA Land, a gallon of regular was 25/30 cents before the 1st embargo. After it ended, the price jumped to a buck.

After the 2nd embargo ended, price rose to a buck 25. Long gas lines, some stations ran out of gas during long gas lines. Some stations restricted amount of gas people could buy.

Odd/even days that gas could be bought based on odd/even license plate numbers. It was a FIASCO!

It paid to know someone who owned or worked at a gas station, could sneak in late at night, fill up. Worked for me!

 

I believe the relevant dimensions are the same, but I know the "whole works" is not identical: brakes etc. The 3.54 is the way to go but relatively hard to find as that ratio was usually found under a 460 auto truck. Maybe cheaper to swap gears (and carrier) into your housing. I went from a 4.56 to a 3.73 via that route and gained a lot of cruising speed. The swap also emphasized the inadequacy of the brakes...! Also, a lot of that engine noise is due to the fan; try it with the fan off and you'll see (and hear) what I mean.
Eric

 

460 introduced in 1973 F100/350's, A/T (C6) & 2WD only thru 1982. All 1968/78 Passenger Car 460's: C6 only.

1953/65 F250: 12 1/8" x 2" front/rear drum brakes.

12" x 2 1/2" front/rear drum brakes introduced in 1966 F250's, standard equipment in Camper Specials and F250's with 7500 & 8100 GVWR's.

1968/72 F250 2WD's with optional dual piston caliper front disc brakes: 12" x 2 1/2" rear drum brakes.

Other 1966/72 F250's with GVWR's of 6100/6200/6300 lbs. came with 12 1/8" x 2" front/rear drum brakes.

Self adjusting brakes introduced in 1967 F250's. 'Course they only worked (if they worked at all!), when you backed up and stepped on the brake pedal.

 

yes they made both those gears good luck finding them though they are out there just keep looking my advice you can ease up a little bit on your rpms by using an oversize tire i personally use 265 75 16s but thats on a half ton thats sits low i cannot fit a 285 75 16 it rubs the inside of the wheel well .......beginning math rant skip to other dots for final numbers..... 30" and 32" tall tires 4.10 gears..... 30" tire equals 94.2" per revolution 32" tire is 100.48".............. 1000 rpm / 4.10 = 243.9 rpm * 94.2" = 22,975.6 inches per minute(24,507" for 32") divide by 12 to change into feet (30=1914.63)(32=2042.25)divide by 5280 to exchange into miles (30=.3626)(32=.3868)multiply by 60 to get mph at/per 1000 rpm (30=21.76 mph)(32=23.21 mph) .......................doesn't sound like much at first but that's at 3000 rpm that's (30=65.28 mph)(32=69.63 mph) 4.35 mph difference drops around 200 rpm just that much less gas to use..................... i had the 352 and 4 speed in mine with 4.10s and tried to squeeze every ounce of mileage i could out of it i found that it was around 2000-2500 rpm was the butter zone for drivability and fuel mileage and i too decided that 4.10s are great for working just not fuel mileage oh and 30" tires in (3.54 is 75.6 mph at 3000) and (3.73 is 71.75 at 3000 rpm) so jumping from a 30" to a 32" tire is like throwing 3.73 gears into your truck

 

I plan to put 235 85R 16s on it. At present it has 9.50 x 16.5s (somewhat worn) & that looks like a smaller tire than the 235s

 

This is the original tire size used on 1966/79 F250 & 1967/79 F350 Camper Special's with 16.5" x 6.75" wheels.